1. Field of the Invention
The present invention relates to openable, screw-clamped pressurized receptacles for flammable and other dangerous fluids and, more particularly, to a safety device for the clamping screw, or screws, of a pressurized fluid receptacle which is designed to prevent the inadvertent loosening of the screw from the receptacles under internal fluid pressure.
2. Description of the Prior Art
Certain receptacles for pressurized fluids, particularly the housings of liquid filters which operate under pressure, need to be of the screw-clamped type, so as to be accessible through the removal of a housing half or housing cover. This applies especially to filters for fuel and other flammable liquids and to filters for hot and/or chemically aggressive liquids, for example.
Serious damage, including personal injury, can result from the inadvertent opening of such a fluid receptacle while under pressure. The accident risk is particularly high in the case of fuel filters which have a filter housing consisting of a housing base and a housing cap clamped to the housing base by means of a single central clamping screw.
An inadvertent person who proceeds to unscrew the central clamping screw of the fuel filter under pressure would find pressurized fuel squirting from all sides of the filter housing which, if the spill is taking place in the vicinity of a hot internal combustion engine, for example, could easily result in a serious accident.
The elimination of this risk calls for a safety device which is capable of positively preventing the inadvertent unscrewing of the clamping screw, or screws from the pressurized receptacle. Such a safety device is preferably so designed than an attempted removal of the device for access to the clamping screw clearly signals the presence of pressure in the receptacle by opening a tiny bleed passage through which a small amount of pressurized fluid is released. This warning release permits the operator to immediately reset the safety device.
A device which operates in this fashion is known from the German Offenlegungsschrift No. 32 17 371. This prior art safety device, intended for use in conjunction with fuel filters of marine engines, features a safety cap which, in its normal position, surrounds the hexagonal head of the filter clampin screw. A threaded shaft, extending from the inner end wall of the safety cap, engages a threaded throughbore of the clamping screw.
The safety cap can be raised by unscrewing it from the clamping screw to expose the facets of the clamping screw for engagement by a wrench. The action of unscrewing the safety cap establishes a bleed passage connecting the inner end of the throughbore of the clamping screw with the outside. This bleed passage is formed by an inclined bleed bore in the threaded shaft of the safety cap which leads from the outer extremity of the shaft to a point on the shaft which moves above a sealing face on the screw head, when the safety cap is unscrewed a certain distance.
An inwardly crimped edge on the lower extremity of the safety cap and a snap ring near the upper extremity of the clamping screw cooperate to render the safety cap captive of the clamping screw.
Among the shortcomings of the described prior art device are its complexity and cost, inasmuch as the device requires a deep-drawn cap part and a threaded shaft part with an upset head portion to which the cap part is resistance-welded. The consequent need for arranging the safety cap in a captive relationship with the clamping screw complicates the assembly operation, because it requires that the crimping operation on the edge of the safety cap be performed, after the safety cap is screwed onto the clamping screw.